sedimentary
Sandstone Concretion
Ferruginous Sandstone Concretion
Hardness: 6.0-7.0 (on Mohs scale); Color: Reddish-brown, tan, or ochre due to iron oxides; Luster: Dull or earthy; Structure: Clastic, often shows concentric banding; Cleavage: None; Specific Gravity: 2.2-2.8
- Hardness
- 6
- Color
- Reddish-brown, tan, or ochre due to iron oxides
- Luster
- Dull or earthy
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Physical properties
Hardness: 6.0-7.0 (on Mohs scale); Color: Reddish-brown, tan, or ochre due to iron oxides; Luster: Dull or earthy; Structure: Clastic, often shows concentric banding; Cleavage: None; Specific Gravity: 2.2-2.8
Formation & geological history
Formed by the precipitation of mineral cement (usually hematite or limonite) within the spaces between sediment grains. These typically form early in the burial history of the sediment and can range from millions to hundreds of millions of years old.
Uses & applications
Commonly used as decorative garden stones, architectural accents, or as educational specimens for teaching lithification and chemical precipitation in groundwater.
Geological facts
Concretions are often mistaken for fossils, eggs, or meteorites due to their unusual shapes. The reddish-brown 'rind' is often harder than the interior material due to higher iron concentration.
Field identification & locations
Identify in the field by their rounded or nodular shapes that differ from the surrounding bedding. Look for concentric layers of different colors. They are common in arid sedimentary basins and riverbeds.
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